Crystal mounting



Dec. 28, 1948. Q H. s. BATES ET Al;

CRYSTAL MOUNTING Filed Feb. 27. 1945 INVENTORS HHROLD 5. 8/7756 H'NDSHMUEL f7. ROB/NJON IBY THE/R nqzlvr Patented Dec. 28, 1948 Harold s.Bates, Philadelphia, as Samuel A. Robinson, Upper Darby, Pa., assignorsto Philco Corporation, Philadelphia, Pa... a corporation of PennsylvaniaApplication February :1, 1m, Serial N6. 519,088 I 4 Claims. (01?111-3231) invention relates broadly to piezo-electric crystal apparatusand has special reference to improved mounting means for such crytsals.

The principal object of the invention is the provision of improvedholding or mounting means for piezo-electric crystals, particularly ofthe type provided with plated electrodes.

Another and important object of the invention is to provide apiezo-electric crystal mounting exemplified by its extreme simplicityand maximum economy of manufacture.

The piezo-electric eflect of certain crystals is well known incrystallography and a detailed discusion thereof has been omitted hereinas being unnecessary to a clear understanding of the present invention.However, it may be well to point out that to utilize this piezo-electriceffect it is usually necessary to drive the crystal through the mediumof a pair of electrodes, one on each side of the crystal in directcontact with the main faces or surfaces thereof. When the crystal isused in its original cut condition the electrodes are usually 'providedby the crystal mounting elements, however, the crystal in many cases isprovided with so-called plated electrodes, in other words the electrodesare provided by plating the opposite main surfaces, either wholly or inpart,

2 taken substantially along the plane of line 2-2, Fig. 1;

Figure 3 is an exploded perspective view of the plated crystal and itsring-like holding or mountbers shown in Figure 3, asin their assembledrelation; and

' nates generally an insulating housing member.

with some suitable metallic substance such, for 1 example, as gold orsilver. the plated type electrode produces more uniform performance inmaintaining the rated vibrational frequency of the crystal than do otherknown types of electrodes, and it is with this plated type ofpiezo-electric crystal that the pr 1'sent invention is particularlyconcerned.

There are at least three common well known types of mountings or holders.for piezo-electric crystals, namely, the rod or clamp type, wire typeand air gap type. A detailed description and discussion of the relativemerits of these mountings may be had by reference to The Bell BystemTechnical Journal, volume XXIII, l lo. 2, published April, 1944. Thepresent invention provides a new type of holder which, for the sake ofdistinction, may be designated as a ring or. "washer" type.

To this end the invention contemplates the It has been found that use ofa pair of ring or washer-like members between which the plated crystalis held in the manner clearly illustrated in the accompanying drawings,in which:

Figure 1 is a perspectiveview of a crystal unit embodying the invention;I

Figure 5 is a side elevational view of the assembled members asillustrated in Figure 4. Referring more particularly to the details ofthe drawings, wherein is illustrated one embodiment of the invention,the numeral l0 desigwhlch may conveniently comprise a block ii of somesuitable insulating material, such as polystyrene. The block I I isprovided with a centrally located aperture or bore i2 extending.

therethrough from one face 13 to the opposite face ll, said bore beingclosed at both faces by fiat conductive members I1 and i8 securedthereto, as by screws l9. Conductive members I! and II are provided attheir lower ends with portions 20 and 2i respectively which are turnedinwardly beneaththe bottom wall 22 of housing Ii. These inwardly turnedportions are provided with short conductive prongs 23 and 24,respectively, which provide means for connection of I the crystal unitwith associated apparatus, not shown.

Positioned within bore I! of housing ii, as shown more clearly in Figure2, is a piezo-electric crystal 2! provided at its two opposite majorsurfaces, as indicated by the numerals 2] and 28, with a pair ofadherent metallic coatings or films which comprise the electrodes forthe crystal. These coatings orillms may be plated on the crystal by anyknown method. It is well known in crystallography that thepiezo-electric effect may be obtained from many different crystals andit is the intent of the present invention to include within its scopeall those crystals with which the novel ring-type mounting may be used.

In particular accordance with the present invention the crystal isclamped between a pair of ring or washer-like members 28 and 30 to thus,form a three-element unit as more clearly depicted in Figures 3, a and5, said unit being positioned within the left end of bore II, as seen inFigure 2, with ring 28 in direct contact with conductive plate II. Theclamping pressur is provided by a resilient member Ii, such as the coilspring shown, positioned within bore l2 between ring 30 and conductiveplate ll. In the Figure ills a vertical sectional view of said unit" asevent that the frequency of the crystal is suiiiciently high to createan objectionable inductive effect in the coil spring, other resilientmeans, such as a spring leaf, may be employed. It may be seen byreference to Figure 5 that the ring members 29 and 30 clamp the crystalat the corners only, thus leaving the central portion thcrcof free tovibrate. One of the advantages of this type of mounting means is therestriction or damping of unwanted modes of vibration to an extentpreventing serious dips in activity characteristic, over a widetemperature range. It will be noted, by reference again to Figure 2,that rings 29 and 30, in conjunction with the conductive plates H and i8and prongs 23 and 21, provide means for connecting the plated crystal tothe associated apparatus, spring 29 being conductiveiy interposedbetween ring 30 and plate l8.

With particular reference to Figure 5 it may be seen that the diagonaldimension of the crystal 25 is preferably equal to the outside diameterof the ring members 29 and 30. Now, with reference to Figure 2, it willbe noted that the diameter of bore i2 is equal substantially to that ofthe outside diameters of said rings, thereby preventing accidentalchanges in the position of said crystal with relation to the rings,should the unit be subjected to shocks. Thus it will be evident that thecentral area, i. e. that area of the crystal free to vibrate, willremain fixed and hence without variation in its activity. With the aboveto the crystal while at the same time permitting the free area of saidcrystal to vibrate with the desired activity and at its rated frequency.

It should be particularly understood that the rings 29 and 30 may bemade by a simple inexpensive stamping method, sufficient care beingtaken to provide the side of the ring contacting the crystal electrodewith a continuous plane surface, whereby each of said corners may beclamped by at least a portion of this surface regardless of the angularorientation of the crystal in the plane of the rings.

This plane surface may, if desired, encompass the whole side area of thering-like members, however, it will be evident that it is not essentialthat the corners of the crystal be clamped by the full overlying ringsurface, as illustrated in Figure 5, as a lesser portion thereof may besufficient. It is necessary only that one side surface of each ring beprovided with a continuous plane surface. It is to be understood howeverthat both is sides of said ring-like members may be provided with such aplane surface it such is desired, thereby facilitating the assembly ofthe unit by eliminating the necessity of first determining which sidethereof has been so provided.

It is further evident that the exterior configuration of housing II ismerely illustrative and may assume other convenient forms withoutdeparting from the spirit of the invention. Similarly, the mountingrings or washers need not necessarily be circular, and the use of thewords annular" or ring-like" in the appended claims, should beunderstood with this in mind.

From the foregoing description it is now clearly evident that there hasbeen provided by the above described invention, a novel improvedmounting means for piezo-electric crystals and one which is exemplifiedby its extreme simplicity and economy of manufacture.

We claim: I

1. In combination, a rectangular piezo-electric crystal having oppositesubstantially parallel major surfaces, said surfaces being metalized andforming electrodes, and mounting means com prising a pair ofsubstantially circular metallic members each having a continuous annularplane surface between which surfaces the crystal is clamped, saidannular plane surfaces contacting corner portions of adjacent metalizedmajor surfaces of said crystal.

2. A piezo-electric crystal unit comprising a rectangular piezo-electriccrystal of the type having plated electrodes on its opposite majorsurfaces, a pair of metallic ring-llke members each having a continuousannular plane surface, a housing and means within said housing clampingsaid crystal between said members with at least a portion of each cornerof said plated major surfaces in intimate contact with a portion of theadjacent annular plane surface.

3. A construction in accordance with claim 2 in which the majordimension of said crystal is substantially equal to the major dimensionof said members, and in which said housing is so constructed andarranged as to closely encompass said members and said crystal in amanner preventing displacement of the crystal with relation to saidmembers.

4. In combination, a rectangular plezo-electric crystal having op ositemajor surfaces, mounting means comprising A pair oi substantiallycircular members each having a continuous annular plane surface betweenwhich surfaces the crystal is clamped, said annular plane surfacescontacting corner portions of the adjacent major surface of saidcrystal, each of said members further being substantially co-extensivein major dimension with the major dimension of said crystal, and acylindrical housing closely encompassing said members and being in closeadjacency to the corners of said crystal, whereby to preventdisplacement of said crystal with relation to said members.

HAROLD S. BATES. SAMUEL A. ROBINSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,047,387 Scott July 14, 19362,327,487 Bach Aug. 24, 1943 2,390,048 Bach Dec. 4, 1945

